The present invention relates to an electronic key system.
Japanese Laid-Open Patent Publication No. 2001-311333 describes an electronic key system that improves the security level and convenience for an automobile. The electronic key system is provided with a smart ignition function that enables the starting of the engine when an authentic key is carried into an automobile. An automobile employing the electronic key system has a rotary switch or push button to start the engine. When the starting of the engine is enabled, the driver turns a knob of the rotary switch to a start position or pushes the push button to start the engine.
The electronic key system includes an electronic key (portable device), which is held by the driver, and an engine start controller, which is installed in the automobile. The portable device stores an ID code that is unique to the portable device. The engine start controller stores an ID code (automobile ID code) that is identical to the ID code of the portable device. The engine start controller performs bidirectional communication with the portable device. When the two ID codes match, the engine start controller enables the starting of the engine.
More specifically, when the door of the automobile is open, the engine start controller transmits a request signal in a range covering most of the passenger compartment to perform bidirectional communication with the portable device. When a driver carrying the portable device enters the passenger compartment, the portable device transmits a signal including the ID code in response to the request signal. Then, the engine start controller determines whether the ID code of the portable device matches the automobile ID code. If the two ID codes match, the engine start controller validates the smart ignition function to enable the starting of the engine.
The smart ignition function enables the engine to be started just by carrying the portable device into the automobile and operating the engine start switch. That is, there is no need to perform a burdensome key operation to start the engine. This improves convenience. In addition, the portable device, which is difficult to duplicate compared to conventional mechanical keys, is necessary to enable the starting of the engine. This improves the security level of the automobile. Further, an electronic key system provided with the smart ignition function normally includes an immobilizer function. The engine cannot be started when the immobilizer function is valid. Predetermined operations are performed with the portable device to invalidate the immobilizer function and enable the starting of the engine.
The portable device, which is used for the smart ignition function, includes a battery functioning as a power supply. Thus, if battery drainage occurs, the portable device does not transmit the signal including the ID code in response to the request signal from the engine start controller even if the driver is carrying the portable device when entering the automobile. In this case, bidirectional communication is not performed between the portable device and the engine start controller. Thus, the smart ignition function remains invalid. In such a state, the driver must invalidate the immobilizer function by performing the predetermined operations with the portable device to start the engine.
The portable device includes a transponder. The transponder stores a transponder code that is unique to the transponder, or the portable device. The engine start controller stores a transponder code (automobile transponder code) that is identical to the transponder code of the portable device. When the two transponder codes match, the engine start controller invalidates the immobilizer function and enables the starting of the engine.
More specifically, if the engine start switch is a rotary switch, the driver inserts the portable device in an electronic key insertion slot located in the knob of the rotary switch. A key detection switch detects the insertion of the portable device. As a result, the engine start controller transmits a transponder activation signal to the vicinity of the engine start switch. In response to the transponder activation signal, the portable device transmits a signal including the transponder code. The engine start controller then determines whether the transponder code of the portable device matches the automobile transponder code. When the two transponder codes match, the engine start controller invalidates the immobilizer function and enables the starting of the engine. In a state in which the starting of the engine is enabled, that is, when the portable device is inserted in the electronic key insertion slot of the engine start switch, the driver turns the knob of the engine start switch to the start position in order to start the engine.
If the engine start switch is a push switch, the driver pushes the engine start switch when the smart ignition function is invalid. This transmits the transponder activation signal in the vicinity of the engine start switch. In a state in which the transponder activation signal is being transmitted in the vicinity of the engine start switch, the driver holds the portable device near the engine start switch. As a result, in response to the transponder activation signal, the portable device transmits a signal including the transponder code. The engine start controller then invalidates the immobilizer function and enables the starting of the engine. When the starting of the engine is enabled, the driver pushes the engine start switch again to start the engine.
As described above, when the smart ignition function is valid, the starting of the engine is enabled just by carrying the portable device into the automobile. When the smart ignition function is invalid due to a reason such as battery drainage, predetermined operations must be performed to enable the starting of the engine.
However, circumstances such as battery drainage does not often occur. Thus, even if the driver is aware that predetermined operations are necessary, the driver may forget the specific operations. Thus, there is a necessity to instruct the driver of the operations that must be performed when the smart ignition function is invalid.